1. Field of the Invention
The present invention relates to a method for coating soot on a melt contact surface, particularly that of an injection sleeve for casting, a plunger end face or a mold cavity, to improve the flow of the melt, maintain the temperature of the melt, or improve the parting property.
2. Description of the Related Art
In various casting and forging processes such as a die casting process, a squeeze casting process, and a melt forging process, if a melt has direct contact with a melt contact surface such as the inner surface of a mold cavity or injection sleeve or a plunger end face, the parting property of a product from the mold is degraded and an advance or retreat of a plunger tip is not smooth. Accordingly, a parting agent is coated on the melt contact surface before the casting operation is carried out.
For example, water-soluble Hitasol (trademark) has been used as the parting agent. However, since the parting agent of this type is water-soluble, the temperature of the surface on which the parting agent is to be coated should be maintained at a temperature as low as about 100.degree. to about 250.degree. C. Furthermore, the amount deposited of the parting agent differs according to the temperature of the surface to be coated and the conditions are not stable. Moreover, in order to shorten the cycle time, water cooling becomes necessary and shortening of the cycle time is limited, and there is a problem of a long cycle time. Still in addition, since the main component of the parting agent is water-solubilized crystalline graphite, the heat conductivity is high and the temperature-maintaining property is not good, and the melt is readily cooled and running of the melt is worsened. If the concentration of the parting agent is increased so as to improve the temperature-maintaining property, the spray nozzle is readily clogged and the conditions become unstable.
Under this background, an injection method using a molding machine was proposed, in Japanese Unexamined Patent Publication No. 61-99551. According to this method, a lubricant or parting agent is coated on a melt contact surface, soot is coated thereon by a burner, a melt is supplied, and mold clamping and injection are then carried out. In this method, the temperature-maintaining property is imparted over the temperature-maintaining property attained by using only the parting agent, the time required for solidification is prolonged, and running of the melt is improved. Furthermore, an effect is attained of drastically reducing the amount of gas generated.
In this conventional injection method in a molding machine where soot is coated on a melt contact surface, however, a satisfactory result cannot be expected with respect to the adhesion of soot to the melt-contacting surface, and soot must be recoated at each shot cycle, and therefore, the productivity is reduced and a great deal of labor is required.
Further, since the space between the injection nozzle and the surface to be coated is opened, soot is scattered around to contaminate the working environment or cause an inhalation of soot by workers, and it is difficult to maintain a good working environment. This problem also arises when a ceramic powder or the like is coated as the parting agent instead of soot.